Most automobiles require, in terms of terminal arrangement, one of two general types of lead-acid automotive batteries: top terminal and side terminal. Top terminal batteries are provided with terminals, commonly of a post configuration, upstanding through the top wall of the battery cover in two of its corners, usually two corners separated by one of the longer sides of the cover. Examples of such terminal arrangements are disclosed, e.g., in U.S. Pat. Nos. 4,042,762 to D. Hakarine and 3,871,924 to D. DeMattie et al. Batteries must be connected to the automobile with correct polarity. Thus, car manufacturers generally provide terminal connections which are no longer than necessary to ensure proper connection to the battery. Such customized terminal connections, depending on their polarity, require either "left-handed" or "right-handed" batteries, which batteries are identical except for the reversal of terminal polarity. Consequently, many battery manufacturers have produced both kinds. In an effort to standardize, i.e., to produce a single type of top terminal battery which will fit both types of terminal connections, some manufacturers now provide top terminal batteries with the terminal posts located near the ends and near or on the longitudinal center line of the battery cover. Examples of such centered top terminal arrangements are disclosed, e.g., in U.S. Pat. Nos. 4,444,853 to V. Halsall et al. (FIGS. 11-12); 4,278,742 to T. Oxenreider et al.; and 4,371,591 to T. Oxenreider et al. By centering the top terminals near or on the longitudinal center line and by rotating the battery 180 degrees as needed, centered top terminal batteries accommodate both left- and right-handed terminal connections.
Batteries having side terminals constitute a second type of battery. In such batteries, the terminals generally are located near the top and ends of a vertical sidewall, usually the longer sidewall of the battery container or cover. Typically, side terminals are threaded to accept connector bolts which fasten the terminal connections to the terminals. The location of side terminals, however, typically makes it difficult to connect the terminal connections. Examples of such side terminal batteries are disclosed, e.g., in Halsall '853 (FIGS. 9-10); U.S. Pat. Nos. 4,304,827 to W. Clingenpeel; 4,272,592 to S. Miyagawa; and 4,143,215 to V. Mocas.
In a further effort to standardize batteries to fit both top and side terminal requirements, some manufacturers have made or proposed dual terminal batteries. Although the name is somewhat of a misnomer because it implies that the battery has two terminals, dual terminal batteries actually have four terminals: a pair of top terminals and a pair of side terminals. Examples of dual terminal batteries are disclosed, e.g., in U.S. Pat. No. 4,424,264 to M. McGuire et al. and Japanese Pat. No. 56-175964. Particularly when the top terminal pair is centered i.e., situated on or near the longitudinal center line of the battery, dual terminal batteries in theory can achieve great success in standardization. For that reason, they represent a substantial advance in the art and potentially a significant means for reducing the large, costly inventories which battery manufactures and retailers must maintain.
Regardless of the arrangement of their terminals, however, lead-acid batteries typically share certain features. The electrochemical components commonly are set within a solid right rectangular shaped container made of an injection molded thermoplastic, such as polypropylene. The interior of the container is divided by partition walls into a series of cells and within each cell is disposed an electrode stack in contact with electrolyte, e.g., a sulfuric acid based electrolyte.
The electrode stacks comprise alternate positive and negative plates and a separator between each adjacent plate pair. The positive and negative plates of each cell stack are connected in parallel, respectively, by positive and negative conductive straps. The electrode stacks in turn are connected in series by at least one intercell connection between the conductive straps. The conductive straps of each inner cell group generally have one such intercell connection, although multiple intercell connections are known. The conductive strap in each of the two end cells is a terminal conductive strap, and is, as the name implies, electrically connected to the positive and negative plates and the corresponding positive or negative battery terminals typically through, inter alia, an element post integrally formed with the respective terminal conductive strap.
Regardless of the terminal arrangement, bushings generally are used to electrically connect the terminals to the element posts. Typically, they are mounted in the battery cover or container sidewall and are designed to accept and be welded to the element posts during assembly of the battery. Such bushings are disclosed, e.g., in Halsall '853 (in top and side terminal batteries); McGuire '264 (in dual terminal batteries); and Japanese Pat. No. '964 (in dual terminal batteries). The terminals themselves, in the case of the side terminals, typically comprise hard metal, threaded nuts cast into the side terminal bushings. The top terminals, on the other hand, generally result from the fusion of end portions of the lead-alloy, top terminal bushing with the lead or lead-alloy element posts or are a separate piece subsequently attached to the welded bushing and element post. The bushings should conduct electricity to the terminals efficiently and with sufficiently high rates. Moreover, to the extent possible in dual terminal batteries, electrical conduction to one set of terminals should not be compromised in favor of the other set of terminals.
The bushing also must not create or exacerbate the problem of electrolyte and gas leakage from the interior of the battery to the ambient. Generally speaking, electrolyte to some degree may creep along each seal between each part of the battery, especially if there is an imperfect seal. More specifically, electrolyte creepage can occur at the plastic to plastic heat seal between the battery container and cover, between the bushings and the plastic, and between the bushings and the element posts. While electrolyte creepage is a problem in all types of lead-acid batteries, it is a more acute problem in wet, maintenance-free, dual terminal batteries.
In recombinant, as compared to wet batteries, there is substantially no free electrolyte in the cells. The major portion of the electrolyte, i.e., approximately 70%, is restrained in the highly absorbent microfine glass fiber separator material between the positive and negative plates. Accordingly, there is less electrolyte creepage because the electrolyte, in effect, is immobilized to a significant degree. In wet batteries electrolyte generally fills the cells to a level substantially above the top of the cell plates, especially in maintenance-free wet batteries where excess electrolyte is necessary to ensure long service life. The problem of electrolyte creepage, therefore, is a major concern because the electrolyte tends to splash and slosh through the interior during transportation, installation, and use of the battery.
Dual terminal batteries, because they comprise side terminals as well as top terminals, are particularly prone to leakage because the side terminals typically are mounted through a vertical sidewall of either the container or the cover. For that reason, the seal between the bushing and plastic in a side terminal is located lower than that in a top terminal and, therefore, nearer to and generally below the electrolyte level. Moreover, if the terminal is mounted through the cover sidewall, the seal between the cover and container also must be lower and, therefore, closer to and generally below the electrolyte level as well.
Electrolyte creepage not only reduces the amount of electrolyte in the cells, but it can corrode the terminals and impair conductivity to the terminal connections as well. The acid in the electrolyte also is harmful to skin, clothing, and other materials which it contacts.
Gas leakage, however, also poses problems. Gases evolved while charging the battery can leak through the various seals, particularly around the bushing if the weld to the element post is faulty. A faulty weld between the bushing and the element post also may result in a gap which may allow electricity to arc.
Additionally, both electrolyte and gas leakage tend to increase over the life of the battery. The battery is subject to ordinary wear and tear, principally caused by vibration from the vehicle in which it is installed. Additionally, during the life of the battery, the plates tend to grow, i.e., they expand and, via the terminal conductive straps and element posts, can stress the element post/bushing weld. In the course of shipping and installation the battery typically is subjected to rough treatment and mishandling as well, e.g., dropping the battery or knocking or overtightening the terminal connections. Consequently, the various seals in the battery deteriorate and become more susceptible to leaking. Rough treatment not only weakens and breaks the various seals, but also may cause the bushing to break. Moreover, a break in the bushing or in the bushing/terminal weld may result in a gap which allows electricity to arc.
To summarize, dual terminal batteries having centered top terminals are preferred over conventional side and top terminal batteries because such dual terminal batteries can be mounted in a wider variety of vehicles. Unfortunately, despite the clear need for a reliable dual terminal battery and primarily due to the design of their bushings, such batteries do not appear to have achieved a high degree of success in eliminating electrolyte and gas leakage. Moreover, the seal between the bushing and plastic and between the bushing and element post and the bushing itself has tended to deteriorate and/or break during service. Additionally, dual terminal designs should provide equal electrical conduction to both sets of terminals, however, because of cover design limitations, they are difficult to make and assemble. Side terminals of some dual terminal batteries also are inaccessible and make it difficult to connect the battery to side terminal connectors.
An object of this invention, therefore, is to provide a dual terminal battery having centered top terminals, which battery comprises a bushing which serves to reduce electrolyte and gas leakage.
A further object of this invention is to provide such a battery with a bushing which has increased strength and durability;
Another object of this invention is to provide such a battery with a bushing which conducts electricity to both sets of terminals with substantially equal efficiencies and rates.
Yet another object of the present invention is to provide such a battery to which side terminal connections may be easily connected.
Other objects of the present invention will become apparent to those skilled in the art upon reading the following detailed description and upon reference to the drawings.